Defective Microwave Photonic Crystals for Salinity Detection

In this paper, defective microwave photonic crystals (MPCs) are designed to sense the salinity of aqueous solutions. The defective MPC sensors are constructed by two kinds of microwave dielectric layers and one defective salt solution layer. Transfer matrix method (TMM) for lossy medium is developed to calculate the transmittance spectra of the sensors. It is found that the peak transmittance of both the defective resonance within the microwave band gap (MBG) and transmitting modes outside the MBG monotonously decrease with the increase of salinity, while the resonant and transmitting mode frequencies remain unchanged. By comparing the four MPC sensor structures, the first transmitting mode in the upper frequency band outside the MBG of the 15-layer MPC sensor has the largest salinity sensing range from 0 to 40‰ with relative stable detecting sensitivity. The sensing principle is based on the fact that the dielectric loss factor of saline solution is much more sensitive to salinity than the dielectric constant in the microwave frequency band. The sensitivity, quality factor, and salinity detection range of the MPC sensors are calculated and compared. The reported defective MPC sensors are suitable to be used for non-contact salinity detection.

Detecting a Stroke-Affected Region in the Brain by Scanning with Low-Intensity Electromagnetic Waves in the Radio Frequency/Microwave Band

There is a compelling need for a new form of head scanner to diagnose whether a patient is experiencing a stroke. Crucially, the scanner must be quickly and safely deployable at the site of the emergency to reduce the time between a diagnosis and treatment being commenced. That will help to improve the long-term outlook for many patients, which in turn will help to reduce the high cost of stroke to national economies. This paper describes a novel scanning method that utilises low-intensity electromagnetic waves in the radio frequency/microwave band to detect a stroke-affected region in the brain. This method has the potential to be low cost, portable, and widely deployable, and it is intrinsically safe for the patient and operator. It requires no specialist shielding or power supplies and, hence, can be rapidly deployed at the site of the emergency. That could be at the patient’s bedside within a hospital, at the patient’s home or place of work, or in a community setting such as a GP surgery or a nursing home. Results are presented from an extensive programme of scans of inanimate test subjects that are materially valid representations of a human head. These results confirm that the scanning method is indeed capable of detecting a stroke-affected region in these subjects. The significance of these results is discussed, as well as ways in which the efficacy of the scanning methodology could be further improved.

DESIGNING MICROWAVE BAND ATTENUATORS AS ELECTRIC FILTERS WITH LOSSES

This paper presents the results of modeling attenuators with an attenuation of 1,2 dB and 1,8 dB, based on a harmonic filter with resistive inserts. Resistive inserts were introduced into the low-resistance sections of the harmonic filter, and resistive loops were connected to the high-resistance sections of the filter. An implementation of a 10 dB attenuator based on a quasi-polynomial bandpass filter with losses is proposed. The working frequency band of such attenuators reaches 4 GHz.

Effect of Some Meteorological Variables and Conditions on Mobile Phone and 'TV' Satellite Signal

The study aimed to seek for the effect of meteorological parameters and conditions on wave transport for both radio wave band that used by mobile phone communication and microwave band that used in 'TV' satellites by showing which atmospheric variable and conditions have a positive or negative effect on signal strength. Data of study was recorded perfectly from one selected point by hand using the same devices for all recording to exclude the error caused by changing device types. The results showed that atmospheric conditions had a noticeable effect on microwave signal band that used by 'TV' satellite especially when there was a rainy case, and for atmospheric 'UV' index it had a direct positive effect on radio waveband used by mobile phone because there was an increase in signal strength corresponding with increasing of 'UV' index (from 1 to 5 of UV index range). For temperature, the result showed inverse proportion with radio waveband signal, but relative humidity didn't show up any relations with both study band's signals. Day time variation of signals was recorded for both wavebands, the result of radio waveband signal fluctuated in semi sine wave shape but with decreasing trend along day time, and for 'TV' satellite microwave band signal the result recorded increasing trend along day time, and this may because of solar radiation activity but in general, the satellite band signal was higher affected by weather condition as compared with mobile phone radio wave signal band.

A nested square-shape dielectric resonator for microwave band antenna applications

In this paper, a nested square-shape dielectric resonator (NSDR) has been designed and investigated for antenna applications in the microwave band. A solid square dielectric resonator (SSDR) was modified systematically by introducing air-gap in the azimuth (ϕ-direction). By retaining the square shape of the dielectric resonator (DR), the well-known analysis tools can be applied to evaluate the performance of the NSDR. To validate the performance of the proposed NSDR in antenna applications, theoretical, simulation, and experimental analysis of the subject has been performed. A simple microstrip-line feeding source printed on the top of Rogers RO4003 grounded substrate was utilized without any external matching network. Unlike solid square DR, the proposed NSDR considerably improves the impedance bandwidth. The proposed antenna has been prototyped and experimentally validated. The antenna operates in the range of 12.34GHz to 21.7GHz which corresponds to 56% percentage bandwidth with peak realized gain 6.5dB. The antenna has stable radiation characteristics in the broadside direction. A close agreement between simulation and experimental results confirms the improved performance of NSDR in antenna applications.

A Modified Formula for Calculating Dielectric Properties of Granular Agricultural Products in the Microwave Band

Dielectric properties are important characteristic parameters in the microwave-assisted application of hygroscopic agricultural media. To break through the limitation of traditional general effective medium (GEM) formula and develop the new calculation formula suitable for agricultural products, a modified formula, that is, modified general agricultural products effective medium (abbreviated as MGAPEM) formula, was presented in this study for the dielectric property calculation of granular agricultural products in the microwave band. The correctness, validity, and accuracy of MGAPEM formula were verified by using literature and experimental measurement data. Results show that the maximum errors of the dielectric constant and dielectric loss factor are 0.42% and 0.98%, respectively, in the conditions of microwave frequency (2.0–12.2 Ghz) and moisture content (2.0%-19.7%, wet basis). The accuracy of MGAPEM is higher than some traditional theoretical formulas. The MGAPEM formula provides a theoretical formula for the dielectric property analysis of granular agricultural products in the microwave band at room temperature (24℃).